Trying to up-level this discussion yet again, I believe that we
haven't yet either clearly distinguished the hypothetical "canonical"
format from the hypothetical "archival" format, or clearly
established the requirements for each of them.
If the requirements came out to be identical, that would be
excellent, but it seems unlikely to be the case.
In the end, the canonical format may turn out to be an
abstraction, and the real-world requirement is something that
is functionally equivalent to the canonical format. By contrast,
the archival format MUST [RFC2119] be some kind of physical
analogue or digital representation that can be filed away in a
library or museum.
Down level again, draft-hoffman-rfcformat-canon-others-02 seems
to assume that XML is a stable format, unlike HTML. I'm not so sure
about that; we might have to regress another level and say that
our format is defined in SGML (even if, in practice, it is based
on a specific version of some dialect of SGML such as a current
version of XML or HTML).
Regards
Brian Carpenter